Anti-cavitation means for marine propulsion device

Claim 1

In a marine propulsion device having an outboard drive unit with an internal chamber in communication with a source of gas, a rotatable propeller carried by said drive unit and having an inner hub, an outer bub spaced therefrom to define a primary annular passage therethrough in communication with said chamber to pass substantially all of said gas from said chamber out the rear of the propeller, and at least two blades extending radially outwardly from said outer hub forward of said propeller rear; the improvement comprising secondary passage means to provide communication from said passage to an area adjacent the face of each of said blades to release a minor amount of said gas from said passage along the root of each of said blades such that any vacuum therealong is relieved, said secondary passaGe means including at least one aperture in said outer bhub associated with each propeller blade, said aperture being positioned adjacent to the face of its associated blade.